1. Field of the Invention
The present invention relates to a vertical cavity surface emitting laser diode (hereafter simply denoted as VCSEL) and a method to form the VCSEL.
2. Relater Background Art
Nishiyama et al. has reported one type VCSEL in Electronics Letters, vol. 39(5) (2003) pp. 437-439, in which the VCSEL provides, on the InP substrate, a Bragg reflector (hereafter simply denoted as DBR) formed by a combination of AlGaInAs and InP, an active layer, an n-type InP layer to bury a tunnel junction region with a mesa shape, and another Bragg reflector (DBR) made of multi-layered dielectric film. The mesa shaped tunnel junction region is formed by an etching of a heavily doped p-type layer and a heavily doped n-type layer.
The VCSEL described above provides the mesa shaped tunnel junction region after the formation of double layers of the heavily doped n-type and p-type layers; accordingly, the height of the mesa for the tunnel junction region inevitably increases, substantially a sum of two heavily doped layers. Because an n-type InP layer grown so as to cover the tunnel junction region shows a step with a comparable height, and the multi-layered dielectric film for the DBR is formed on this n-type InP layer with the larger step, the step in the surface of the n-type layer causes scattering of the light generated in the active layer, which degrades the performance of the VCSEL. Thus, the present invention is to provide a structure for the VCSEL to reduce the light scattering within the optical cavity and to provide a method to form the VCSEL.